The present invention is with respect to a way of measuring reflectance of radiation at a reflecting surface in a field of measurement, using a transmitter producing a beam of radiation and a receiver for the beam after undergoing reflectance. Furthermore the invention has to do with forms of apparatus for measuring reflectance at a reflecting surface using a transmitter and a receiver.
Reflectance measurements are undertaken for the purpose of measuring reflectance of light reflecting surfaces so that readings may be taken for such reflectance or changes therein and a quantitative record may be produced. Measurements of this sort, to be exact, have so far been very greatly dependent on the distance the reflectance surface to be tested, that is to say from the distance the field of measurement is from the transmitter and/or the receiving surface. Because the reading produced for the intensity of the reflected beam and for this reason the outcome of measurement is very highly dependent on the distance between the reflectance surface or the field of measurement and the transmitter and/or the receiving surface, in the case of normal or prior art processes and apparatus for reflectance measurement a question of key importance is having the surface to be tested or measured (that is to say the field of measurement) at a highly reproducible distance from the receiver and/or the transmitter. In the case of a known reflectance photometer (see German Offenlegungsschrift specification No. 3,011,223) very complex means had to be used for keeping to the desired distance between the field of measurement and the receiver or transmitter and for making certain that exact adjustment to this distance was possible on setting up the apparatus. The use of such a known apparatus is very complex and only well trained persons come into question for the operation thereof, and even so there is still the danger of false readings being taken.